DE69231368T2 - Cross sealing device for a packaging machine - Google Patents

Description

Background of the invention

This invention relates to a thermal cross-sealer for closing a packaging material, which is used in packaging machines for simultaneously filling a bag with articles, such as food, and producing a packaged product.

A bag-making packaging machine which simultaneously forms a bag filled with articles such as food and produces a packaged product therefrom, such as a so-called column type packaging machine, can close the superposed long side edges of a web-like elongated packaging material (hereinafter referred to as film) while converting this film into the shape of a bag by means of a forming device and then, while drawing the tubularly formed film, transversely close the lower end of the film by means of a pair of thermal transverse closing devices arranged under the outlet of the filling cylinder used for filling the tubular film with articles to be packaged. Since such a packaging machine can simultaneously and continuously form bags and fill them with articles to be packaged, it is considered to be an apparatus with high processability.

Japanese Patent Publication Tokkai 235006/87 discloses a so-called rotary drive type apparatus which can cause the heating surfaces of its cross-sealing means to come into contact with the film while the cross-sealing means are moved linearly in the direction in which the film is drawn, so that a sufficiently long period of time can be spent on the cross-sealing operation even if the period of time of the cyclic packaging operation. However, in order to make the cross-sealing devices move in a straight line trajectory, this device uses D-shaped grooves to guide these devices while forcing them to move cyclically. In other words, their straight line trajectory and the pressure force between them are uniquely determined, and the film may be subjected to an inappropriate force from them depending on the thickness, material behavior and/or width of the film. Consequently, the film may be damaged or the device may fail to reliably perform a cross-sealing operation.

Packaging machines of the so-called intermittent drive type are also known. They are simpler in construction, although they are disadvantageous in terms of reducing the period of cyclic movement, and they are characterized by intermittently pulling the film and carrying out the transverse closing with the film stopped. The method of using a hydraulic (oil pressure) cylinder is known in this connection for pressing the transverse closing devices against each other and for adjusting the pressing force between them by regulating this pressure cylinder. However, such a cylinder tends to enlarge the device as a whole, and the problem of keeping the cylinder oil away from the objects to be packaged arises.

In view of the above, the present invention has been designed to substantially eliminate the problems discussed and to provide an improved closer and an improved packaging machine, wherein the pressing force with which the transverse sealing means sandwiches the film between them during thermal sealing to close the bag can be adjusted to a predetermined level depending on the thickness, width and material property of the film which finally forms the bag, the structure being compact and eliminating any possible Contamination of the items to be put into the bag, which would otherwise result from the use of the oil, can be avoided.

According to the invention there is provided a cross-sealer for a packaging machine for closing a bag in a cross-direction after the bag has been filled with articles to be packaged, the bag being made from a web-like elongated film which moves on a transport path in a film transport direction, the cross-direction being transverse to the film transport direction, and the cross-sealer comprising:

a pair of transverse sealing means mounted for rotation about spaced apart substantially parallel axes, the pair of transverse sealing means being disposed downstream of a bag forming means for forming the film into a predetermined shape to form a bag and disposed opposite one another on opposite sides of the film transport path; and

a pressure adjusting device for moving the pair of cross-sealing devices in an approach-distance direction both toward and away from each other, to thereby sandwich the film at a certain closing position thereon for thermal closing, and for maintaining a pressing force between the pair of cross-sealing devices at a certain level;

wherein the pressure adjustment device comprises:

an approach-distance motor for driving the axes of the pair of cross shutters in the approach-distance direction;

a device for detecting an angle of rotation of the cross-closing devices about the axes; and

a control device which causes the approach-distance motor to rotate at a certain moment during a closing period at which the pair of transverse closing devices press the film between them at the a predetermined closing position and rotating at a speed independent of a moment during a period of time other than the closing period, the closing period being determined by the detecting device.

The pressure adjusting device comprises an approach-removal motor for driving the pair of cross-sealers in the approach-removal direction; and a control device for causing the approach-removal motor to rotate at a certain moment while the pair of cross-sealers sandwich the film therebetween at the certain closing position.

According to the invention, during thermal sealing, the pressing force exerted by the transverse sealing means on the bag to be sealed can be maintained at the predetermined level, and therefore accurate thermal sealing can be achieved which is suitable with respect to the thickness, width and/or material property of the film used to form the bag. In addition, since the motor replaces the hydraulic cylinders used heretofore in the prior art machines, the machine can be assembled as a whole in a compact size and substantially free from any possibility that the objects to be filled in the bag may be contaminated with oil.

In a preferred embodiment of the present invention, the pressure adjusting device comprises: a pair of movable frames movable in an approach-distance direction in which the pair of transverse closing devices move toward and away from each other, each supporting one of the transverse closing devices and receiving the reaction force of the pressing force; and a rectilinear motion-to-rotary motion converting device for converting the relative motion between the pair of movable frame into a rotary motion due to the reaction force. The approach-distance motor is operable to move the pair of movable frames toward and away from each other in the approach-distance direction by the rectilinear motion-to-rotary motion converting means.

In another preferred embodiment of the present invention, at least one of the pair of transverse closing means is provided with a return means which urges the one transverse closing means in the direction of the other of the pair of transverse closing means by an elastic restoring force proportional to the deformation of the return means. Thus, the pressing force applied to the bag by the transverse closing means during thermal closing can advantageously be evenly distributed during thermal closing over each local area of the bag where thermal closing is carried out.

In another preferred embodiment of the present invention, the pressure adjusting means is operable to cause the pair of transverse sealing means to thermally seal the bag while the transported bag is held stationary.

Short description of the drawings

Fig. 1 shows an oblique view of a packaging machine of a column type with a cross closer according to a first embodiment of the invention.

Fig. 2 shows a front view of a section of an arm rotation mechanism of the closer from Fig. 1.

Fig. 3 shows a structural diagram of the mechanism for moving the axis of the arm in the closer from Fig. 1.

Fig. 4 shows a block diagram of an example of the control operation for the closer from Fig. 1.

Figures 5a and 5b show timing diagrams for the basic cross-closing mode of operation of the closer of Figure 1.

Fig. 6a and 6b show timing diagrams for the final acceleration mode of the cross-closing operation of the closer from Fig. 1.

Fig. 7a and 7b show timing diagrams for the transverse mode of operation with tightening by the closer from Fig. 1.

Fig. 8a and 8b show timing diagrams for the final acceleration mode of the transverse closing operation with tightening by the closer from Fig. 1.

Fig. 9 shows a front view of a detail of an essential portion of a cross-locking mechanism according to a second embodiment of the invention.

Fig. 10 shows an illustration of the principles of the cross-closing mechanism from Fig. 9.

Fig. 11 shows a schematic representation of the structure of a transverse closing jaw, which is a variant of the second embodiment of the invention.

Fig. 12 shows a schematic representation of the structure of a transverse closing jaw, which is another variant of the second embodiment of the invention.

Detailed description of the preferred embodiments

Embodiments of the invention are described below with reference to the accompanying drawings.

Fig. 1 shows a column type packaging machine equipped with a transverse sealing mechanism according to a first embodiment of the present invention. This packaging machine is of the type having no filling cylinder and is constructed such that after a web-like film S is bent into a tubular shape by a forming device 2 under a hopper 1 to make bags therefrom, a pair of pull-down belts 3 each arranged thereunder with a suction chamber 4 pull its outer surface by suction to keep it in the cylindrical shape while longitudinal sealing is carried out along its superimposed longitudinal edges a by means of a longitudinal sealer 5. The film S is then conveyed to a transverse sealer 10 which will be described in detail below.

The transverse closer 10 arranged under the pull-down belts 3 is provided for closing the film S in a transverse direction transverse to the direction in which it is transported, and comprises a pair of front and rear rotary arms 11 (serving as rotary drive means) for supporting a pair of the transverse closing jaws 20 which are opposed to each other transversely to the path of the film S so that they always face the same directions and undergo rotary movement with respect to each other in synchronism, and pairs of left and right outer movable frames 30 and inner movable frames 34 which can cause the rotary axes of the rotary arms 11 to move toward or away from each other. The rotary arms are adapted to rotate such that their rotary directions R match the moving direction A of the film S as the pair of the transverse closing jaws 20 approach each other.

As shown in Fig. 2, which shows a detailed sectional view of one of the rotary arms 11, each rotary arm 11 has the shape of a frame having three sides with left and right arms 12 connected to each other by a connecting shaft 13. The end portion of one of the arms 12 is attached to a support shaft 14 which projects inwardly from the movable frames 30 and 34 on one side (the left side in Fig. 2). The end portion of the other of the arms 12 is fixed to a power receiving shaft 15 which projects inwardly from the movable frames 30 and 34 on the other side (the right side in Fig. 2). The rotary arms 11 thus constructed are adapted to rotate about the shafts 14 and 15 by a driving force transmitted through the power receiving shaft 15.

Reference numeral 17 designates sleeves which are rotatably supported around the connecting shaft 13 and serve to support the closing jaw 20. The transverse closing jaw 20 for thermally closing the tubular-shaped film S in the transverse direction is attached to these sleeves 17. One of the sleeves 17 is formed integrally with a planetary gear 21. A sun gear 24 is attached to a fixed shaft 23 which penetrates the support shaft 14. The sun gear 24 and the planetary gear 21 have the same number of teeth and are coupled to one another via an idler gear 22.

Denoted by reference numeral 25 is a Schmidt clutch mechanism comprising three disks 25a, 25b and 25c connected by a linkage 26 (shown in Fig. 1). The first disk 25a of each Schmidt clutch mechanism 25 is connected to a drive shaft 27 of an arm rotation servo motor 29 and the third disk 25c of each Schmidt clutch mechanism 25 is connected to the power receiving shaft 15 such that the rotational movement of the drive shaft 27 is connected to the power receiving shaft 15 regardless of changes in the angle of rotation or the transmitted torque or any axial displacement between them. In this way, the pair of rotating arms 11 can rotate in mutually opposite directions by means of intermeshing gears 28 (shown in Fig. 1) mounted on the drive shafts 27 for the Schmidt clutch mechanism 25.

The outer and inner movable frames 30 and 34 support the pair of rotary arms 11 such that the distance between them can be changed. The outer and inner movable frame pairs 30 and 34 are respectively connected to each other near the rear ends by a connecting plate 31 and 35 into the form of a frame with three sides surrounding the rotary arms 11. They are assembled so that the outer movable frames 30 can slide back and forth on a housing main frame 46 and that the inner movable frames 34 can slide back and forth inside each of the outer movable frames 30.

Reference numeral 38 designates a clamping screw which moves the outer and inner movable frames 30 and 34 forward and backward in a coordinated manner so that the cross-locking jaws 20 can be moved on a desired D-shaped trajectory comprising a straight section. As shown in Fig. 3, this clamping screw 38 is axially supported by a frame structure 45 provided between the outer and inner movable frames 30 and 34. The clamping screw 38 has a right-hand threaded portion 38a and a left-hand threaded portion 38b, which are respectively engaged with the connecting plates 31 and 35 for the outer and inner movable frames 30 and 34 via in-line bearings 32 and 36, so that the outer and inner movable frames 30 and 34 can be moved in opposite directions to each other to cause the pair of rotary arms 11 to move toward or away from each other selectively in the positive or negative direction by rotating the clamping screw 38. The in-line bearings 32 and 36 may be of a readily available type having many balls engaging the threaded portions 38a and 38b so as to add a moment to an arm shifting motor 40 or rotate the tension screw 38 in the other direction when a force is applied to the movable frames 30 and 34 in the forward-backward direction X by the reaction force on the Closing pressure is applied. The clamping screw 38 and the bearings 32 and 36 arranged in line can be regarded as a rectilinear-to-rotary motion converting device G for converting the relative motion between the pairs of movable frames 30 and 34 due to the above-mentioned reaction force to the pressing force between the pair of closing jaws 20 into a rotary motion.

For the above-mentioned arm rotation motor 40, which is connected to the tension screw 38 via a tuning belt 39, as shown in Fig. 3, an AC servo motor can be used which can freely switch between torque-controlled and speed-controlled modes of operation. In the torque-controlled mode, the torque of the motor 40 is maintained at a predetermined level regardless of its speed, but this predetermined level can be suitably changed. In the speed-controlled mode, its speed can be made constant regardless of the torque. As will be explained in more detail below, the arm shifting motor 40 is controlled by a control circuit so that it can rotate in either direction in coordination with the arm rotation servo motor 29 for rotating the rotating arms 11 so that the cross-locking jaws 20 each run on a trajectory comprising a straight section of length L, as shown in Fig. 5. In Fig. 1, reference numeral 47 designates a partition plate.

Fig. 4 shows a circuit for controlling the arm rotation servo motor 29 and the arm displacement servo motor 40. Figs. 5-8 show both the movement of the rotary arm 11 and the operation of the arm rotation and the arm displacement servo motor 29 and 40 in different modes of the cross-closing operation. In Fig. 4, reference numeral 51 designates a detector for determining the angle of rotation of the rotary arms 11 from a certain reference position I. This angle is determined from the angle of rotation of the arm rotation servo motor 29 and a value corresponding to the angle of rotation of the A pulse signal proportional to the rotational arms 11 is transmitted by a pulse transmitter 52 which is connected to this detecting device 51 and to a control unit 53. Reference numeral 48 designates a mode selection device such as a keyboard for determining a desired cross-closing mode. Reference numeral 49 designates a film determination device such as a keyboard for determining the material behavior, thickness, width, etc. of the film. One of the available cross-closing modes such as the "cross-closing basic mode" shown in Fig. 5, the "acceleration end mode" shown in Fig. 6, the "cross-closing mode of operation with tightening" shown in Fig. 7 or the "acceleration end mode with tightening" shown in Fig. 8 is predetermined by the mode selection device 48 and the material behavior, width, etc. of the film are predetermined by the film determination device 49. An appropriate program of programs stored in a storage device 55 is loaded therefrom by a loading device 54, and a program signal is output to the control unit 53 and executed. These programs stored in the storage device 55 are prepared for different operation modes and according to different pressure and different stroke distance at the time of closing as explained above.

Since a pulse signal from the pulse transmitter 52 and a mode-dependent program from the storage device 55 are input to the control unit 53, mode setting devices such as those corresponding to the basic mode (53a), the acceleration end mode (53b) and the tightening mode (53c) can be activated. The control unit 53 then outputs control signals to a motor drive device 56 for controlling the rotation of the arm rotation servomotor 29 so that the angular velocity of the rotary arms 11 is changed during the transverse closing operation, and to another Motor drive means 57 to control the timing for switching the arm shift servo motor 40 so that the positions of the rotation axes of the rotary arms 11 are changed during the transverse closing operation. The movable frames 30 and 34, the linear motion-to-rotary motion converting means G, the arm shift servo motor 40, and the control unit 53 can be regarded as a pressure adjusting means H. Since the length of the transverse closing operation (i.e., the stroke distance) changes when the rotation centers of the rotary arms 11 are shifted, the rest of the foregoing elements without the linear motion-to-rotary motion converting means G (i.e., the movable frames 30 and 34, the arm shift servo motor 40, and the control unit 53) can be regarded as a stroke adjusting means J.

The operation of the system thus constructed will be described below. First, it is assumed that the basic cross-closing mode as shown in Fig. 5a with the cross-closing length indicated by L1 has been selected by the mode selecting means 48 and that a material behavior and a thickness of the film S have been predetermined by the film determining means 49. In response, a program for such basic cross-closing mode corresponding to the predetermined material behavior and the thickness of the film S is selected from among the many programs stored in the storage means 55 and loaded by the loading means 54. The basic mode setting means 53a is activated in accordance with the loaded program, and the arm shift servomotor 40 starts rotating in the positive direction after the rotary arms 11 start rotating from the initial position I and they reach the initial position II for the cross-closing operation as shown in Fig. 5a. Then, the arm shift servo motor 40 rotates in the negative direction from the center point III until the rotary arms 11 reach the end point IV of the transverse closing operation, so as to move the pair of rotary arms 11 away from and toward each other via the outer and inner movable frames 30 and 34. which are engaged with the clamping screw 38. In the meantime, the film S is superimposed between the pair of transverse clamping jaws 20 and moved at the same value as its normal running speed.

Consequently, the closing jaws 20 supported at the ends of the rotary arms 11 begin to come into contact with the surface of the film S, that is, to run in straight lines. During this operation, the arm shift servomotor 40 is operated in the torque-controlled mode so that its torque is maintained at a predetermined constant level T, as shown in Fig. 5b. Thus, the pressing force on the film 5 from the closing jaws 20 can be kept constant as much as possible. In the meantime, the arm rotation servomotor 29 allows the rotational speed of the rotary arms 11 to be varied according to the torque applied thereto to cause the closing jaws 20 to move along the film S, thereby effecting the transverse closing. During this operation, the rotation centers of the rotary arms 11 supporting the clamping jaws 20 move in the front-back direction X, thereby balancing the torque of the clamping screw 38 due to the reaction force to the above-mentioned pressing force against the constant moment T₀ of the servo motor 40, so that the pressing force is maintained at a constant level. This constant level of the pressing force can be adjusted by changing the size T₀.

When another cross-closing basic mode with a shorter stroke distance L2 is predetermined, the arm shift servo motor 40 starts to rotate in the positive direction according to the corresponding program as shown by chain lines in Figs. 5a and 5b, thus shifting the rotation center from 0 to 0', and thereafter causes the clamping jaws 20 to move on a shorter straight path between the points II' and IV'.

If the user selects the final acceleration mode to accelerate and decelerate the jaws 20 at the beginning and end of the cross-closing, the setting device 53b is activated for the final acceleration mode. In this mode, the arm shifting servo motor 40 is gradually accelerated to gradually shift the positions of the rotation centers of the rotary arms from 0 to 0' as shown in Fig. 6 before the start point II is reached. After the end point IV is reached, the motor 40 is gradually decelerated. In other words, the program for this mode provides an acceleration range from II' to II and a deceleration range from IV to IV' as shown in Fig. 6b. In this mode, both sudden release of the pair of rotary arms 11 at the start point II of the cross-closing and sudden approach at the end point IV can be avoided and the cross-closer 10 can generally operate more smoothly.

The tightening mode setting device 53c is activated when the user predetermines the tightening mode shown in Fig. 7, wherein, prior to transverse closing, the articles inside the film S are "tightened" or caused to fall down so that they do not become caught between the closing jaws 20. In this mode, the control unit 53 causes tightening plates 61 to be pressed against the film S by means of springs 60 when the rotating arms 11 are still separated from each other (at the tightening starting point II') before they reach the transverse closing starting point II. Thereafter, the tightening plates 61 are caused to move faster than the film S, thereby tightening the film S until the center point III (the tightening ending point) is reached. At that moment, the center of rotation of the rotating arms 11 is moved from B to C, thereby causing the closing jaws 20 to press against each other. From this moment on, the arm displacement servo motor 40 is operated in the torque-controlled mode until the end point IV of the cross-closing is reached, so that the closing jaws 20 are moved by the same value as the normal speed of the path through the film S. With the cross-closing device 10 operated by such a program This prevents objects to be packaged from becoming caught between the closing jaws 20 and the closing process can be carried out reliably.

When the final acceleration mode with tightening is predetermined, as shown in Fig. 8, the closer 10 is operated with a program that provides an acceleration range from II' to II before the starting point of tightening and a deceleration range from IV to IV' after the end point IV for transverse closing.

As explained above with reference to the embodiments described with reference to Figs. 1-8, since the pair of the closing jaws 20 (serving as the transverse closing means) are caused to run along a straight line trajectory along the path of the film S by the above-mentioned pressure adjusting means (H), transverse closing can be carried out with the film S continuously moving. Since the pressing force between the pair of the closing jaws 20 can be maintained at a constant level corresponding to a set magnitude of the moment T0 on the arm shift servo motor 40, the film 5 can be suitably transversely closed according to its thickness, material properties, etc. Since the stroke distance and hence the time period of the closing operation can be suitably selected by the stroke adjusting means J according to the thickness and material properties of the film S, the closing operation according to the invention can be even more suitably carried out.

Since the above-mentioned pressure adjusting device H has both the function of moving the pair of closing jaws 20 on a desired trajectory and the function of maintaining the pressure between them at a constant level, the closer 10 as a whole can be constructed more simply than if these two functions were carried out by two different mechanisms. Since the motor 40 takes the place of a hydraulic cylinder , the shutter 10 can be made more compact, and the possibility of contamination of the articles to be packaged by oil can be eliminated. The shutter 10 according to the invention can also be made compact because the pairs of outer and inner movable frames 30 and 34, the arm shift servomotor 40 and its control unit 53, which form a portion of the above-mentioned pressure adjusting device H, also serve as the above-mentioned stroke adjusting device J. Instead of the above-mentioned device G for converting a linear motion into a rotary motion with a tightening screw and in-line bearings, an alternative mechanism with a link mechanism or grooved cams may also be used.

Fig. 9 shows a second embodiment of the present invention, which is characterized in that the support mechanism for the jaws 20 is improved by adding a return means. As shown in Fig. 9, in which the above-described components are designated by the same reference numerals, the lower ends of support springs 71 (serving as a return means) are attached to the inner edges of the pair of sleeves 17, which are rotatably supported by the connecting shaft 13 between the arms 12. These springs 71 are cantilevered and are provided for the purpose of applying a uniform pressing force to the film S over its entire width W. Their free ends extend inwardly toward each other and are attached to a jaw 20.

With the return device 71 thus provided, even if the closing jaws 20 incline like a seesaw, since the longitudinally closed edge portions of the film 5 abut against it when the closing jaws 20 are pressed against each other, these support springs 71 are individually bent and provide a restoring force proportional to their deformation to cause the closing jaw 20 attached to them to return to the opposite Closing jaw 20 returns, thereby applying a uniform pressure force to the film S.

As the pair of the locking jaws 20 move on D-shaped trajectories by the rotation of the arms 12 of the rotary arms 11 and the movement of the movable frames 30 and 34 and reach the starting point of the transverse locking and come into contact with each other with the film S superimposed between them, the locking jaws 20 experience a force tending to move them around the longitudinally locked edges of the film S. When the locking jaws 20 experience such a force, each of the support springs 71 is bent according to the displacement of the locking jaws 20. At the same time, the reaction forces from the support springs 71 are applied back to the locking jaws 20 so as to uniformly press the film S to perform the transverse locking.

This operation will be explained in more detail with reference to Fig. 10, which shows the pair of closing jaws 20, between which a film S is superimposed, the longitudinally closed edges a of which are formed in three or four layers. In this situation, at least one of the pair of closing jaws 20 will assume an inclined position like a seesaw around the longitudinally closed edges a. This inclination can be expressed as a function of the deformations of the springs 71. The deformation δ is given by a formula as follows:

δ = pA³/12EI = pD³/Ebt³ (1)

where D is the effective length of the cantilevered support spring 71, t is the thickness and b is the sheet width of the spring, 2p is the load and E and I are the elastic modulus and the second order area moment of the spring 71, respectively. Its reaction force R is indirectly proportional to the deformation 71 and is given by

R = Ebt³δ/D³ (2)

specified.

Thus, when the deformation of the left and right support springs 71 are δ1 and δ2, respectively, their reaction forces R1 and Rr proportional to δ1 and δ2, respectively, are applied to the locking jaw 20 toward the other locking jaw 20 which is opposite to it.

For example, if a load of 500 kg is considered to be applied to a support spring 71 of effective length D = 44 mm, sheet thickness t = 5 mm, sheet width b = 18 mm and elastic modulus = 2.1 x 10⁴ kg/mm², this will cause a deformation of 0.5 mm and 0.4 mm of the left and right springs 71, respectively. Formula (2) then shows that the support spring 71 on the left side has a reaction force R₁. = 278 kg on the closing jaw 20 and that the support spring 71 on the right side exerts a reaction force Rr = 222 kg on the closing jaw 20 in the direction in which it returns to the normal position, which provides a locally uniform pressure on the film 5 and restores the deformations in the spring 71.

Fig. 11 shows a support spring of another form. A lock jaw 20A according to this embodiment has an inwardly extending slot 72 formed at each of its side portions, and the portions separated by these slots from the main body of the lock jaw 20A are formed as cantilevered elastic support spring portions 73.

Fig. 12 shows a support spring of yet another form. A locking jaw 20B according to this embodiment is formed as a hollow structure with an elastic hollow housing structure 200 so that the deformation of the locking jaw 20B is canceled by the reaction force which is proportional to the bending of the housing structure 200 itself. A fluid 75 with a low melting point, such as lead, can be enclosed inside the hollow interior 74 of the housing structure 200 to provide a uniform heat balance at the locking jaw 20B. In a In such a situation, the housing structure 200 serves as the above-mentioned return means. The support springs 71 and 73 and the hollow elastic structure 20B may also be used only as one of the pair of the locking jaws 20.

The above-described embodiments 1 and 2 of the present invention relate to cross-sealers of the type which causes the sealing jaws to move on generally circular trajectories so that cross-sealing can be effected while the film S is continuously transported by the pull-down belts 3.

Although the above-described embodiments 1 and 2 of the present invention all relate to a transverse sealer used in a vertical column type packaging machine, it should be understood that the transverse sealer of the present invention can also be used in a horizontal column type packaging machine. In addition, the transverse sealers of the present invention can also be used in a packaging machine of a three-side sealing type in which the film can be folded in two layers, its superimposed edges can be closed vertically lengthwise and then it can be transversely closed at two places, and in a four-side sealing type in which vertical sealing can be carried out at two places along the superimposed edges and also along the opposite side and then transverse sealing can be carried out at two places.

Industrial applicability

It also goes without saying that the present invention can be applied not only to machines for packaging foodstuffs, but also to packaging machines for industrial parts or products.

Claims (4)

1. A transverse closer for a packaging machine for closing a bag in a transverse direction after the bag has been filled with articles to be packaged, the bag being made from a web-like elongated film (5) moving on a transport path in a film transport direction, the transverse direction being transverse to the film transport direction (A), and the transverse closer comprising: a pair of transverse closing devices (20, 20) mounted for rotation about spaced apart substantially parallel axes (14, 15), the pair of transverse closing devices being arranged downstream of a bag forming device (2) for forming the film into a predetermined shape to form a bag and being arranged opposite one another on opposite sides of the transport path of the film; and a pressure adjusting device (H, H1) for moving the pair of cross-sealing devices (20, 20) in an approach-distance direction both toward and away from each other to thereby sandwich the film (S) at a certain closing position thereon for thermal sealing and for maintaining a pressing force between the pair of cross-sealing devices (20, 20) at a certain level; wherein the pressure adjustment device (H) has the following: an approach-distance motor (40, 40A) for driving the axes of the pair of cross-closing devices (20, 20) in the approach-distance direction; a device (51) for detecting an angle of rotation of the transverse closing devices about the axes; and a control device (53, 103) which causes the approach-distance motor (40, 40A) to rotate at a certain moment (To) during a closing period, wherein the pair of transverse closing means (20, 20) sandwich the film (S) therebetween at the predetermined closing position, and rotate at a speed independent of a moment during a period other than the closing period, the closing period being determined by the detecting means. 2. Cross-closing device according to claim 1, wherein the pressure adjustment device (H, H1) comprises: a pair of movable frames (30, 34) movable in an approach-distance direction in which the pair of transverse locking devices (20) move toward and away from each other, each supporting one of the transverse locking devices (20, 20) and receiving the reaction force of the pressing force; and a rectilinear-to-rotary motion converting device (G) for converting the relative motion between the pair of movable frames (30, 34) due to the reaction force into a rotary motion; wherein the approach-distance motor (40, 40A) is operable to move the pair of movable frames (30, 34) toward and away from each other in the approach-distance direction through the rectilinear-to-rotary motion converting means (G). 3. A cross-closing device according to claim 1 or 2, wherein at least one of the pair of cross-closing devices (20, 20) is provided with a return device (71, 73, 200) which urges the one cross-closing device (20) in the direction of the other of the pair of cross-closing devices (20) by an elastic restoring force which is proportional to the deformation of the return device. 4. Packaging machine for producing a packaged product by forming a bag and filling the bag with articles, the packaging machine comprising the cross-closer (10) according to one of claims 1 to 3.